<html>
<head>
	<title>Basic Concepts</title>
	
	<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>

	<!-- navigation header start -->
	<table width="100%">
	   <tr>
	      <!-- back --><td width="50px"><a href="about_en.html">Prev</a></td>
	      <!-- home --><td style="text-align:center;"><b>Basic Concepts</b></td>
	      <!-- next --><td width="50px;" style="text-align:right;"><a href="subscriptions_en.html">Next</a></td>
	   </tr>
	</table>
	<hr />
	<!-- navigation header end -->

	<!-- content start --> 
	<p>
	This section tries to clarify some of the technical jargon used
	along with feed readers.
	</p>
	
	<h3>What does "online/offline desktop" news aggregator mean?</h3>
	<p>
	Feed readers or news aggregators can be realised as web applications
	or as desktop applications. The place of execution (your computer
	vs. some webserver) implies certain advantages and disadvantages.
	</p>
	
	<p>
	A <b>desktop news aggregator</b> runs on your own PC and stores 
	aggregated feeds locally. It accesses each news feed and downloads
	its newest headlines periodically. Note that not all desktop news 
	aggregators can work offline. Some desktop aggregators retrieve 
	feeds each time you access them instead of caching them for later
	use. Liferea as an <b>offline capable</b> desktop aggregator caches
	feeds and is suitable for use with portable devices (laptops, hand 
	helds...) that do not have a permanent internet connection.
	</p>
	
	<ul>
	    <li><b>Disadvantages:</b>
	         <ul>
		     <li>No implicit state synchronization when used from different client machines</li>
		     <li>Higher bandwidth usage compared to online aggregators</li>
		     <li>Need to be installed on each client machines</li>
		     <li>OS-dependant</li>
		 </ul>
	    </li>
	    <li><b>Advantages:</b>
	         <ul>
		     <li>Your cached feed contents are saved on your own (secure) machine.</li>
		     <li>Your cached feed contents are searchable locally with other tools (e.g. <a href="http://beagle-project.org/Main_Page">Beagle</a>)</li>
		     <li>Your feed list is not accessible to 3rd parties</li>
		     <li>Each feed access are done in private.</li>
		 </ul>
	    </li>
	</ul>

	
	<p>
	A <b>online news aggregator</b> (for example <a href="http://bloglines.com">Bloglines</a>)
	is run on a remote webserver which you can access from everywhere
	as long as you have network access. When you log in to the online
	news aggregator it usually doesn't need to fetch the most recent
	headlines of you feed subscriptions because it implements feed 
	caching	to save bandwidth.
	</p>
	
	<ul>
	    <li><b>Disadvantages:</b>
	         <ul>
		     <li>You rely on some 3rd party vendor for the news aggregator service.</li>
		     <li>Often you have to pay for premium features.</li>
		     <li>No chance to improve/modify/fix the online application.</li>
		     <li>You need a web browser to access it.</li>
		 </ul>
	    </li>
	    <li><b>Advantages:</b>
	         <ul>
		     <li>You get the same feed list and feed states no matter from where you access them.</li>
		     <li>Practically no bandwidth usage except for the access of the web interface.</li>
		     <li>Community headline rating systems to categorize content.</li>
		     <li>Sharing headlines with the community (or specific users).</li>
		 </ul>
	    </li>
	</ul>
	
	<h3>What is a Feed?</h3>
	<p>
	For a news aggregator a <i>news feed</i> is a distinct information source. A
	news aggregator usually retrieves <i>news headlines</i> from many news feed <i>subscriptions</i>.
	The term "news feed" is not very precise as feeds can also provide weblog 
	postings, podcasts and practically every type of content. The same goes for the
	term "news headlines": often "article" or "post" would be a
	better description. Nonetheless the prefix "news" is usually used with the terms
	"feed", "headline" and "aggregator".
	</p>
	
	<h3>What is a Subscription?</h3>
	<p>
	When you add a new feed then you have to specify the source of the 
	feed, so that the news aggregator can initially retrieve it. The feed source
	is usually a HTTP URL. This URL with optional authentication and proxy
	settings is a "subscription" managed by Liferea.
	</p>	
	
	<h3>What is the Feed List?</h3>
	<p>
	To manage and easily navigate your subscriptions Liferea provides you with
	a hierarchic tree of your subscriptions. Similar to email clients the "feed
	list" is located in the left pane. You can organize your subscription 
	after topics in different folders.
	</p>
	
	<h3>What is a Headline?</h3>
	<p>
	When a news aggregator updates a news feed it downloads the source document
	from the source URL of the feed subscription. This source document provides
	a set of the most recent headlines which then need to be merged against the 
	current feed cache of the aggregator because the set of headlines provided
	by the feed source changes over time.
	</p>
	<p>
	Headlines as provided by the feed source are the smallest information
	unit handled by aggregators.
	</p>
	
	<h3>What is the Item List?</h3>
	<p>
	In Liferea headlines are also called <i>items</i> and are presented
	in the so called <i>item list</i>. Following the email client paradigm
	the item list is often presented in the upper right pane in the news
	aggregator interface.
	</p>
	
	<!-- content end --> 

	<!-- navigation footer start -->
	<hr />
	<table width="100%">
	   <tr>
	      <!-- back --><td width="50px"><a href="about_en.html">Prev</a></td>
	      <!-- home --><td style="text-align:center;"><a href="topics_en.html">Contents</a></td>
	      <!-- next --><td width="50px;" style="text-align:right;"><a href="subscriptions_en.html">Next</a></td>
	   </tr>
	</table>
	<!-- navigation footer end -->
</body>
</html>

